In the design of our novel optical immuno assay, spherical dielectric micro-particles coated with antibody or antigen (Immuno particles) form components of an immunoassay. The spherical dielectric immuno-particle which constitutes a solid-phase, micro-scale immunosensor is confined to an optical trap. Analyte binding to the particle is determined by optical signal transduction using either fluorescence (conventional and/or two-photon excited) or light scattering. Both homogeneous and heterogeneous assays can be performed in direct and competitive binding modes. The optical trap can also be used to assemble several particles varying in size and specific chemistry into 1 or 2 dimensional microsensor arrays (n x n). Each microsensor element can then be addressed ("read") in series using a focused laser beam with beam/stage scanning. Parallel data acquisition can also be accomplished by imaging the entire array field using either image-forming optics or by recording the response of each sensor particle directly on a semiconductor surface. This enables rapid measurements of multiple analytes since each particle constitutes a unique sensor.